Invert photos in Photos desktop app

That still works for me in Big Sur - but it doesn't work the same way as in preview.

You drag the top right point of the line down to bottom right, and the bottom left up to top left. It can be quite tricky to pickup the ends of the line - you have to position the cursor until it changes into a black cross hair.

Also (as shown in the example image in your link) it only inverts the brightness, it doesn't invert the colours. It is no good for colour negative conversion if that is what you want to do.

Which system version do you have installed?

On macOS 11 Big Sur you have to set the Curves to show the RGB Curve, then grab each dot at the end of the curve and drag it into the opposite direction. If you do not grab the endpoints, the curve will change its shape. If that happens, I would click the button "Reset Adjustments" at the bottom of the Adjustment panel to start over.

It invert the colours as well, invert each of the color lines R, G, B as well.

Interesting - but from my experiment - if you want inverted clours AND brightness (colour negative look), you only invert the colour chanels, but leave RGB as is - otherwise the RGB change re-inverts the brightness back to normal.

Also useful if you need to do more than one image, is to do it on one of them, then copy the adjustments to the others.

Hi -

Those instructions describe how to do it with the preview app, not photos. It still works.

When in the edit mode, go to image>copy adjustments. Then go to the other images (one at a time unfortunately, but if they are together in the library - or you put them in an album, you can use the arrow keys to step through) and image>paste adjustments.

Also the keyboard shortcuts work in edit mode.

shift-cmd-C

shift-cmd-V

As shown in the menu.

This is with each of the color channels plus RGB inverted:

Compare to the original: Pink has been turned into cyan, blue into yellow, black to white.